The new AddUserTab command allows you to create new custom favorites tabs in the Material Manager. To use AddUserTab, you pass in a material and a comma-separated list of tab names.

var oActiveScene = Application.ActiveProject.ActiveScene;
var oMatLib = oActiveScene.ActiveMaterialLibrary;
var oMat = oMatLib.CreateMaterial( "Phong", "MyPhong" );

AddUserTab( oMat, "My Faves" );